Delamination Resistance of Adhesively Bonded European Hornbeam (Carpinus betulus L.) for Structural Applications

Climate change and the transformation of European forests, characterized by an increasing proportion of deciduous species, have encouraged the greater use of a wider range of hardwood species for structural applications. The aim of the present study was to investigate the delamination resistance of locally available hardwood and its suitability for producing glued laminated timber. A total of 15 specimens manufactured from European hornbeam (Carpinus betulus L.) and bonded using a melamine–urea–formaldehyde adhesive system were tested using each of the EN 14080 delamination methods (A and C) to determine their resistance and durability. The obtained mean total delamination was 23.53% for method A and 26.43% for method C, exceeding the EN 14080 acceptance limits. The delamination results did not meet the limits prescribed by the European standard, indicating that the applicability of standardized delamination procedures should be further evaluated using different adhesive systems and manufacturing conditions. Nevertheless, specimens manufactured from the same hardwood and bonded with the same adhesive system have previously satisfied the requirements in shear tests of glue lines, suggesting that delamination and shear tests evaluate different aspects of bond performance. As only one manufacturing configuration of European hornbeam bonded with a melamine–urea–formaldehyde adhesive system was investigated, further research is required before broader conclusions regarding the applicability of standardized delamination procedures to hardwood can be drawn.